A preposition is a word that links a noun or pronoun to some other word in a sentence. Take, for example, these short sentences:

(Up is a preposition connecting went and hill.)

(In is a preposition connecting sat and corner.)

Sing a song of sixpence.

(Of is a preposition connecting song and sixpence.)

The most common prepositions

about	behind	down	off	to
above	below	during	on	toward
across	beneath	except	onto	under
after	beside	for	out	underneath
against	between	from	outside	until
along	beyond	in	over	up
among	but	inside	past	upon
around	by	into	since	with
at	concerning	like	through	within
before	despite	of	throughout	without

Some prepositions (called compound prepositions) consist of more than one word, like in spite of, next to, on top of, and together with.

If you're trying to determine if a particular word is a preposition, here's a little trick that works for many prepositions: See if the word will fit in this sentence:

If the word in question makes sense in that sentence, it's a preposition. (Note that of is the most notable exception.)

Here's another way of remembering what a preposition is. Look at the last eight letters of the word preposition; they spell position. A preposition sometimes tells the position of something: under, over, above, and so forth.

Here's a rule you've probably heard: Never end a sentence with a preposition. Well, sometimes that rule is correct and sometimes it isn't. Generally, your writing sounds better if you can structure a sentence so that it doesn't end with a preposition. However, sometimes you want a more colloquial or conversational tone, and — let's face it — in speaking, we often end sentences with prepositions.

That's the “no-preposition-at-the-end” construction.

That's the way the sentence normally is said.